#encoding:UTF-8

'''
Created on Mar 3, 2014

@author: Wu Botao
'''
import math

def solve():
    x = 0.0
    while(x < 1.0):
        f = -300000.0 \
            + 75000.0/((1 + x) ** 1) + 70000.0/((1 + x) ** 2) \
            + 65000.0/((1 + x) ** 3) + 60000.0/((1 + x) ** 4) \
            + 55000.0/((1 + x) ** 5) + 70000.0/((1 + x) ** 6)
        
        if math.fabs(f - 0) < 1:
            print x
            break
            
        x += 0.000001
       
            
if __name__ == '__main__':           
    solve()
